Q. What is radioactivity and what are alpha particles?
Ans: Radioactivity is the spontaneous emission of energy from unstable atoms.
As you know atoms are found in all matter. There are stable atoms, which remain the same always, and unstable atoms, which break down or 'decay' into new atoms.
These unstable atoms are said to be 'radioactive', because they emit radioactivity from the nucleus as they decay.
The phenomenon of radioactivity is observed in heavy elements such as uranium. Antoine Henri Becquerel, a French scientist discovered radioactivity in 1896 by chance while performing an experiment.
So radioactivity refers to the particles which are emitted from nuclei as a result of nuclear instability.
Alpha particles are fast moving He nuclei which are emitted when a radioactive atom undergoes decay. An alpha particle consists of 2 protons and 2 neutrons. Because it has no electron cloud, it has an overall charge of +2. It is denoted by the symbol α and is written 2 4He2+ or He2+ as there are no electrons.